The goal of this investigation is to describe the molecular events, elucidate the energy sources and identify the membrane constituents which are involved in transfer of bile salts and vitamin B-12 from the lumen of the ileum into the enterocytes. For this purpose we will prepare membrane vesicles derived from intestinal epithelial cells and determine the characteristics of uptake of bile salts and vitamin B-12 by these vesicles. The effects of ions, ion gradients, adenosine triphosphate, temperature, pH, sulfhydryl transport of bile salts and vitamine B-12 will be ascertained. We will also solubilize and purify the bile salt and vitamin B-12 transport systems and incorporate them into phospholipid liposomes. The reconstituted transport system will be utilized to identify the membrane constituents which are responsible for transmembrane transfer of bile salts and vitamin B-12 and to determine how these transport systems interact with other components of the brush border membrane.